It is often necessary to obtain detailed information regarding surface features of components. This can be required in areas that are only accessible by means of remote tooling or equipment. The detailed information may be required to determine if a component is fit for service based on a particular geometric feature. This would include such things as a flaw or surface defect, where a stress analysis would be required to assess if the stresses resulting from this flaw or defect were acceptable.
Replicas are regularly required to help characterize features on surfaces, such as the inside surface of pressure tubes within a nuclear reactor (e.g., a CANDU™ reactor). Pressure tube surface replication in a nuclear reactor is a remote process due to limited access and the presence of high radiation fields. Obtaining high quality surface replicas of flaws with narrow, deep and/or sharp-tipped features is difficult. Obtaining such replicas remotely and/or in wet conditions is even more difficult. Maintaining control of the replicating material during the replicating process is important; it is important that the replicating material is not ‘lost’ into the reactor during the replication process. Due to this handling constraint, a replicating material with moderately high viscosity must be used. Moderately high viscosity facilitates material handling and control, however, the viscous material is more difficult to apply into narrow, deep and/or sharp-tipped features. Trials with less viscous replicating material have not produced satisfactory results because of the difficulty in material handling/control.
Present replicating devices can be delivered to the location of a flaw to obtain a mould impression or replica of the surface feature. Typically, the device carries a quantity of replicating material and is able to apply the material onto the surface. The replicating material is applied in an uncured state, and cures in situ. Once the replicating material has cured, the device containing the replica is retrieved. The geometry of the surface feature is replicated as a negative impression. The replica can be inspected to determine geometric features.
Present replicating devices and processes generally work adequately for broader, open flaws with smoother surfaces and larger root radii. However, existing devices and processes have limited success with flaws that are narrow, deeper, undercut, and have small root radii. A difficulty with flaw replication relates to being able to successfully apply the replicating material into the bottom of the flaw in order to capture its features. In some instances, the replica may not be fully formed, i.e. it does not sufficiently capture the features of the flaw.
When a successful replica cannot be taken, often the worst case assumptions are made when assessing a putative flaw in a reactor pressure tube. Thus, failure to obtain replicas of sufficient quality can result in additional reactor outage time, limitations on the allowable thermal cycles for reactor pressure tubes, and may lead to unnecessary fuel channel replacement.
There remains a need, therefore, for an improved replication device and methods of use of that device.
This background information is provided for the purpose of making known information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.